So last post dealt with NPN transistors and now I show how to deal with the PNP Transistor.
How do you use NPN Transistors
PNP transistors are in essence exactly the same as an NPN transistor but they work in a complementary or mirrored fashion. So rather than applying 0.7V to the base terminal to get the transistor to conduct in this case we need to apply (at the base terminal) 0.7V less than the voltage at the emitter. The diagram below shows how a PNP transistor is used:
Many electronics engineers I know struggle to use PNP transistors because during their training PNP transistors were not covered properly. I know this was the case for me and it's part of the reason I write these blog posts, it's my effort to try to redress the balance. NPN transistors were covered very clearly and we were taught that PNP transistors were the same only in reverse. Technically this is true although I didn't find this obvious at all. I think a better description is that PNP transistor operation is the 'mirror' of NPN transistor operation.
How do you use a PNP transistor?
Well....in my opinion it isn't the same process as designing a circuit with the NPN Transistor! So here we go: to use the transistor connect the emitter to the supply voltage and the collector to the low side of the circuit or the '0V' rail. Next to turn the transistor on and cause current to flow through the transistor we need to apply 0.7V less than what is present at the emitter. Check out the circuits below: